555 Toy Organ Octave (13-keys) build question?

[Jasonmatthew911]

http://i85.photobucket.com/albums/k46/jasonmatthew911/ToyOrganOctave.png


Hey, I'm about to build a 555 Toy organ circuit using (13) 1K trim pots in series, in order to make a properly tuned piano octave...I may add something extra like an active Low-pass filter....I wanted to know if anyone here has built something similar before..I thought I read somewhere that in the schematic I added here, R1 connects to pin 2 of 555 chip and then to an SPDT switch (S9), to switch between 2 capacitor values that go to GND (C1 & C2), which are intended to change the octave or tone...Am I right?...If so, what should be the value of C1 & C2 in order to feel an octave change (up or down) or a difference in tone while the 13 key octave stays in tune?.........Any help and/or advice on this?

[PRR]

> what should be the value of C1 & C2 in order to feel an octave change

2:1 ratio. Switch from 10nFd to 5nFd to get an octave up.

It is hard to find caps with 2:1 values. Instead put two 4.7nFd in parallel, then cut one out for the octave up.

Cap tolerances are very loose, and there are no "trimmer caps" suitable for easy audio. Try to find 2% tolerance caps even if it costs more. However 2% gives over a third of a semi-tone error. You may have to get some caps 100 and 200 times smaller and tack them across the big caps until the octave sounds good.

[Jasonmatthew911]

> what should be the value of C1 & C2 in order to feel an octave change

2:1 ratio. Switch from 10nFd to 5nFd to get an octave up.

It is hard to find caps with 2:1 values. Instead put two 4.7nFd in parallel, then cut one out for the octave up.

Cap tolerances are very loose, and there are no "trimmer caps" suitable for easy audio. Try to find 2% tolerance caps even if it costs more. However 2% gives over a third of a semi-tone error. You may have to get some caps 100 and 200 times smaller and tack them across the big caps until the octave sounds good.

Ok thanks...So,  I can start by connecting R1 directly to C1 that would be .0047uf, then C1 to an SPST  with C2, that would be another .0047uf so that the 2 Caps are in parallel or C2 gets disconnected, right?

[Jasonmatthew911]

> what should be the value of C1 & C2 in order to feel an octave change

2:1 ratio. Switch from 10nFd to 5nFd to get an octave up.

It is hard to find caps with 2:1 values. Instead put two 4.7nFd in parallel, then cut one out for the octave up.

Cap tolerances are very loose, and there are no "trimmer caps" suitable for easy audio. Try to find 2% tolerance caps even if it costs more. However 2% gives over a third of a semi-tone error. You may have to get some caps 100 and 200 times smaller and tack them across the big caps until the octave sounds good.

Also, I forgot to ask...What would be the benefit of using 2% tolerance caps over 10% in this situation?

[PRR]

> using 2% tolerance caps over 10% in this situation?

A musical semi-tone is nearly 6%.

2% caps get you within 1/3rd of a semitone. From C1 to a sharp/flat C2. 10% caps could be one and a half semitones off. From C1 to a sharp/flat B2 or sharp/flat D2-flat.

Either way you have to trim. (Unless you have very loose tuning standards.)

And it isn't a guitar tuning-peg or trim-pot. More like shoving toothpicks and paper under the string to tune it.

Just less tedious to tune the octave if you start with a small error.

And you could get lucky. Two "10%" caps that just-happen to be within 0.5% of each other. That would be OK even if they were 9% off their marked value, since you will trim the pots to hit your reference "A=440" or whatever. With 0.5% difference in caps you are down to 1/11th of a semi-tone error, which is audible but perhaps acceptable in context of a 555 doorbell organ.

[joelindsey]

Just curious, what do you plan on using for the keying switches? I've tossed around the idea of building something like this, a little monophonic bass keyboard with two 555 oscillators tuned an octave apart to fill out the sound a bit more. Sort of like a mini bass combo organ. Never pursued it because I had no idea what to use for keys. 

[Craiz]

I'd opt for little momentary norm-off spst pushbuttons. One of the few things I'd buy from the RatShack.

[Jasonmatthew911]

Just curious, what do you plan on using for the keying switches? I've tossed around the idea of building something like this, a little monophonic bass keyboard with two 555 oscillators tuned an octave apart to fill out the sound a bit more. Sort of like a mini bass combo organ. Never pursued it because I had no idea what to use for keys. 

You can hack an old keyboard that doesn't work and use 1 or 2 octaves off of it, or you can use Arcade buttons, micro switches, any momentary Normally Open SPST push button that doesn't require too much push force basically...If you can't get the keys from a keyboard, arcade buttons might be a good option...I also found these mini squared momentary SPST buttons in white and black that I may give a try, though I think the push force on them is about .3kg...An arcade button only requires about 50 - 75 grams of push force....Hope this helps

We kind of want to build the same thing, except I was gonna build something with 1 octave and add the switch to get an octave higher, but using (2) 555's is a good idea as well, though it means you need 2 octaves of keys or 25 push button switches...

[Jasonmatthew911]

> using 2% tolerance caps over 10% in this situation?

A musical semi-tone is nearly 6%.

2% caps get you within 1/3rd of a semitone. From C1 to a sharp/flat C2. 10% caps could be one and a half semitones off. From C1 to a sharp/flat B2 or sharp/flat D2-flat.

Either way you have to trim. (Unless you have very loose tuning standards.)

And it isn't a guitar tuning-peg or trim-pot. More like shoving toothpicks and paper under the string to tune it.

Just less tedious to tune the octave if you start with a small error.

And you could get lucky. Two "10%" caps that just-happen to be within 0.5% of each other. That would be OK even if they were 9% off their marked value, since you will trim the pots to hit your reference "A=440" or whatever. With 0.5% difference in caps you are down to 1/11th of a semi-tone error, which is audible but perhaps acceptable in context of a 555 doorbell organ.

So I happen to have about 15  - .0047uf Orange drop Caps with 5% tolerance already....I could measure them all and use the 2 that are closest in value to each other, and that would be just as good as the 2% tolerance caps, right?.......Thanks again for all your help PRR

[joelindsey]

Yeah, I've considered junked casio keyboards and such, in a similar fashion of the Melloman (http://mysterycircuits.com/melloman/melloman.html)

The few I've taken apart have these rubbery switch matrices that look like a pain to work with.

When I said two octaves, I didn't mean a two octave keyboard. I meant when you press, say, an E, it plays a low E as well as an E one octave higher, hence the requirement for two oscillators. Combo organs have switches for several octaves, sometimes fifths and thirds in the higher frequencies.

[Jasonmatthew911]

Oh, right on....I know what you mean about the keyboards....You have to find one that isn't such a pain in the ass I guess...I got an Octave off a damaged 5 octave Casio and made a USB/MIDI controller once, using a Gamepad...That keyboard had diodes for each key, if you find that, I think you can replace the diodes with the resistors or trimmers if I'm not mistaken....You'll probably only find keyboards with resistors on each key on an old keyboard from back in the day...

[Jasonmatthew911]

> using 2% tolerance caps over 10% in this situation?

A musical semi-tone is nearly 6%.

2% caps get you within 1/3rd of a semitone. From C1 to a sharp/flat C2. 10% caps could be one and a half semitones off. From C1 to a sharp/flat B2 or sharp/flat D2-flat.

Either way you have to trim. (Unless you have very loose tuning standards.)

And it isn't a guitar tuning-peg or trim-pot. More like shoving toothpicks and paper under the string to tune it.

Just less tedious to tune the octave if you start with a small error.

And you could get lucky. Two "10%" caps that just-happen to be within 0.5% of each other. That would be OK even if they were 9% off their marked value, since you will trim the pots to hit your reference "A=440" or whatever. With 0.5% difference in caps you are down to 1/11th of a semi-tone error, which is audible but perhaps acceptable in context of a 555 doorbell organ.

Hey PRR, I found some 10nf (.01uf) film caps with a 1% tolerance....Would these work better than 2% caps, and what would be the difference if I used 10nf Caps instead of 4.7nf???

[Scruffie]

1% Tollerance is always better than 2%

I had exactly the same project idea and goal as you way back, down to the octave switch so this is very interesting,

[Jasonmatthew911]

Right on...So, if I'm switching between (2) 10nf caps in parallel and (1) 10nf, I should get my Octave up, but it would be an Octave below switching between 4.7nf Caps, right or wrong?

[Jasonmatthew911]

Does anyone know, if I'm tuning my Octave so that my "A" is 440Hz, and I think my "C" would be around 253 or 263Hz around there, don't remember the exact frequency right now...How would (2) 10nf caps in parallel affect that tuning Vs. (2) 4.7nf caps that PRR recommended in parallel?...Would it take my "A" 440Hz to the next lower octave or would my "A" stay at 440Hz?....I ask, because I'd like it so that when my switch is connecting the 2 Caps my "A" is 440Hz, and when I disconnect 1 of the Caps it goes up to the next Octave....I really don't want to go the octave below my "A" 440Hz...I want to go up to the next octave, so I was wondering how (2) 10nf caps would affect this idea, if all my 13 trimmers are 1K, and R1 on the schematic I posted is 10K I think, or should R1 have a different value depending on my Caps used, in order to accomplish the 2 octaves I want?

[PRR]

I picked "10nFd" out of thin air. Hint: that's way small. Study the 555, compute the capacitor to hit your frequency with the resistor(s) you want to use.

[Jasonmatthew911]

I picked "10nFd" out of thin air. Hint: that's way small. Study the 555, compute the capacitor to hit your frequency with the resistor(s) you want to use.

Ok thanks...I'll have to experiment...

[Jasonmatthew911]

I just laid this out on my breadboard, but with 1 switch for now, just to find the Freq. range I want by swapping R1, C1, & C2...I found that with (2) .01uf and R1 being 100K, with 1K trimmer seems to give me the frequency range I wanted...I also felt the octave go up when removing one of the .01uf caps, now I see the reason for the 1% - 2% tolerance caps, but I managed to find 2 caps that were very close to each other in value with some 5% orange drops I had lying around, since my Octave stayed tuned when using both caps, as well as removing a cap, while changing the octave...Thanks PRR ....I know I'm on the right track now.....

By the way, I tried this with a Sanwa Arcade button, and I noticed when ever I push the button there is a light pop or click that gets amplified....I tried a 2M2 resistor to GND in many different spots, but I failed to get rid of the little popping sound when pushing my button...I guess this isn't the same deal as the pull down resistors we use on the inputs of our pedals.....Does anyone have any idea how I can get rid of the light popping sound when pressing the arcade button for my notes??? ...PRR maybe?

[Jasonmatthew911]

By the way...Does the tolerance % of my 1K trimmers matter much in this circuit?....I ask, cuz I noticed that with the 1K alpha pot I tried, sometimes after tuning to the note I wanted, the pitch might shift a little flat or a little sharp after a little while...Not sure if the tolerance % has anything to do with it, or if maybe it would be better to just tune the 1K trimmer to the desired note, then measure it's value and replace with a fixed resistor...

[PRR]

> get rid of the light popping sound
> after tuning to the note I wanted, the pitch might shift a little

Build a "real" organ with a hundred times as many parts. Envelope generators. VCAs. Separate oscillators with high stability parts.

You are doing good for a one-555 organ.